1. Field of the Invention
This invention relates to sensitized record sheet material useful in developing dark-colored marks on contact with colorless ink solutions of chromogenic dye-precursor materials. Such sheet material generally includes an acidic material in the form of a coating on at least one sheet surface. The coating of acidic material serves as a receiving surface for colorless, liquid, solutions of chromogenic compounds which react, on contact, to produce the dark-colored marks.
Acidic materials for use in these record sheet materials have, in the past, included acid or active clay compounds and phenolic resin materials. This invention relates to improved record sheet materials in which neither active clay nor phenolic resin are used.
This invention more particularly relates to the record sheet material coating and to the coating composition. This invention particularly pertains to effective coating compositions used in reduced amounts, without active clay components, and to such coating compositions having an aqueous vehicle at a pH above neutral.
Still more particularly, this invention relates to such coatings from a formulation which includes an aqueous, basic, dispersion of a hydroxy-substituted aromatic carboxylic acid derivative and a Group II metal oxide, carbonate, or phosphate.
This invention, even more specifically, pertains to aqueous, basic, coating formulations, without active clay components, wherein ammonium hydroxide is used to maintain a basic pH, wherein the carboxylic acid derivative is substituted salicylic acid and wherein the metal is zinc. This invention also relates to a record sheet material made using this coating formulation and to the process for making it.
2. Description of the Prior Art
Sensitized record sheet materials are generally known in the prior art. U.S. Pat. No. 3,723,156, issued Mar. 27, 1973, discloses a sensitized record sheet for use with chromogenic compounds wherein the record sheet coating includes an oil-soluble metal salt and an oil-soluble phenolic resin. In the sheet of that patent, there is disclosed to be synergism which results from combination of the metal salt and the phenolic resin. A metal salt disclosed therein, to give some degree of color development, is zinc salicylate.
U.S. Pat. No. 3,767,449, issued Oct. 23, 1973, discloses a sensitized record sheet such as zinc oxide and a carboxylic acid-aldehyde polymer material. Salicylic acid is disclosed to be an eligible carboxylic acid and there is said to be a synergism between the components. The coating is applied from organic solvent systems and in large amounts to yield heavy coatings.
Japanese Disclosure No. Sho 48-51712, dated July 20, 1973, discloses a sensitized sheet wherein the coated components are salicylic acid derivatives combined with zinc or other metal oxide and coated from an aqueous system. The coating weight is high and there is specific teaching that the pH of the coating system must be less than 7.0.
U.S. Pat. No. 3,843,383, issued Oct. 22, 1974, discloses a color developing sheet using an active clay and an aromatic carboxylic acid or alkali metal salt thereof. The sheet of that patent is required to have an active clay which serves as the color developing material and is required to have an aromatic carboxylic acid which apparently serves to stabilize the color, once developed.